Correlation of Hydroxychloroquine Whole Blood Levels With Real and Ideal Body Weight Dosing and Development of Retinal Toxicity.

PURPOSE: To examine the correlation between hydroxychloroquine levels with real body weight and ideal body weight dose and identify patient characteristics at risk for subtherapeutic or supratherapeutic dosing. METHODS: A retrospective chart review of 181 patients with lupus (429 unique hydroxychloroquine whole blood levels) was performed. Hydroxychloroquine levels <100 (indicating medication noncompliance) were excluded (n = 26). Summary statistics, linear regression of hydroxychloroquine level and real body weight/ideal body weight, and odds ratios (ORs) for factors associated with supratherapeutic (>2000 ng/mL) or subtherapeutic (<750 ng/mL) hydroxychloroquine levels were calculated. RESULTS: The correlation of real body weight and hydroxychloroquine level was r = 0.124. Ideal body weight and hydroxychloroquine level had a correlation of r = 0.324. The OR of body mass index (BMI) >30 kg/m2 and supratherapeutic hydroxychloroquine level was 4.95 (95% CI, 1.98-12.39). The OR of BMI <20 kg/m2 and subtherapeutic hydroxychloroquine level was 2.90 (95% CI, 1.58-5.37). Three of 71 patients screened for toxicity had hydroxychloroquine maculopathy. These subjects had mean hydroxychloroquine levels of 1314 ng/mL (range, 1101-1553 ng/mL), 2402 ng/mL (range, 1754-3050 ng/mL), and 1223.8 ng/mL, and BMIs of 20.8 kg/m2, 29.7 kg/m2, and 19.8 kg/m2, respectively. CONCLUSIONS: All dosing schedules show variability in hydroxychloroquine levels. Ideal body weight may correlate more strongly with hydroxychloroquine level than real body weight. Under real body weight-based guidelines, obesity may increase the risk for supratherapeutic hydroxychloroquine levels, and low weight may increase the risk for subtherapeutic levels.